Characterisation of River Bed and Suspended Sediments in the Rio

Journal of South American Earth Sciences I PERGAMON Journal of South American Earth Sciences 12 (1999) 401-410

Characterisation of river bed and suspended sediments in the Rio Madeirai drainage basin (Bolivian Amazonia) Jean LOUPGuyota9*, Jean Marie Jouanneau b, Jean Gabriel WassonC I "IRD, CP 7091, Lago Sul, CEP 71619-970, Brasilia DF, Brazil bDepcirtmeiit Ghologie et Oc&"rcr(,hie, URA 197 CNRS, Uiriiwsité Bordenirs 1, Avetiire des Facrrlt&s, 33405 Talence, Frniice 'CEMAGREF, Laboratoire Hydro-Ecologie Qirarititcitive, BP 220, 69336 Lyon Cedes. 09, Fraiice

Abstract

The grain size distribution of river bed sediments in the Rio Madeira drainage basin shows rapid deposition of the coarser material (> IO mm) as the river flows out of the Andean range to enter the Amazon plain (Llanos). In the Andes, the suspended sediment grain size varies between 0.02 and 0.10 nim in diameter, while in the Llanos the suspended load is dominated by fine silts, between 7 and 13 pm in diameter. In the Llanos, neither the bed sediment nor the suspended sediment varied along a 800 km reach. 0 1999 Elsevier Science Ltd. All rights reserved.

Resumen

La granulometria de los sedimentos transportados sobre et lecho de los cursos de agua (arrastre) demostró que el material mis grueso (> IO mni) se deposita ripidamente en la zona de pie-de-monte. En los Andes, et tamaño del material en suspensión varia de 0.02 a 0.10 nim, mientras que en los Llanos el sedimento transportado es limo fino, con una granulometria entre 7 y 13 pni. En los Llanos, no es perceptible cualquier evolución en el tamaño de los materiales en suspensión, o de los sedimentos de fiindo, de aguas arriba hasta agtias abajo, sobre 800 km. 1999 Elsevier Science Ltd. All rights reserved.

1. Introduction the structure and stability of the bed sediment, as well as water turbidity. Thus sediment dynamics are a key Knowledge about the grain size distribution of the factor in understanding the ecological functioning of river bed and suspended sediment is fundamental to many rivers, especially in the Amazonian area (Sioli, the study of geomorphological process along a fluvial 1984). hydrosystem. Modelling sediment load by means of .The Rio Madeira is the most important southern transport equations, estimating the major and trace el- tributary of the Amazon with a mean annual discharge ement fluxes in the fine fraction transport, understand- of 31,200 m3 s-l (Molinier et al., 1997), and is the ing sediment transfer processes, identifying sediment river that drains the Andean range, the Brazilian shield deposition areas, calculating sedimentation/suspension and the Amazon plains (or "Llanos"). Despite the geo- and waterlsediment discharge ratios, all require good graphical importance of this tributary, data on grain granulometric data. Moreover, the biological com- size distribution are extremely limited for bottom sedi- ponent of river ecosystems is strongly dependent on ment, and totally lacking for suspended sediment matter. The present study aims (1) to provide the results of * Corresponding author. numerous granulometric observations carried out in E-niai1 address: [email protected] (J.L. Guyot). the Bolivian part of the Rio Madeira drainage basin, t"-&siJu ' 0595-9811/99/$ - see front matter 0 1999 Elsevier Science Ltd. All rights reserved. PII: S0895-9811(99)00030-9 -_ al. 401410 402 J.L. Guyot et 1Journal of South American Earth Sciences 12 (1999)

r ~ ~ - - .-q

Fig. 1. PHICAB gauging stations (0)in the Amazonian drainage basin of Bolivia, and sediment sampliiig points along the Rio Beni (see Tables 1 and 2 for station codes).

18,000 2000 and (2) to point out salient features of sediment struc- 1n3 s-l, with a minimum low value of m3 ture characteristics and dynamics along this poorly sL1 and a flood maximum of 52,000 m3 s-’ (Bourges known hydrosystem. and Hoorelbecke, 1995). At Villabella, the sediment Most of the data were collected between 1983 and load is estimated at 230 x 10‘ t yr-’; 72% of the sedi- 1992 within the scope of the Hydrological and ment load is supplied by the Rio Beni and 28% by the Climatological Program of the Bolivian Amazon Rio Mamore, the two main Andean tributaries of the Drainage Basin-PHICAB; ORSTOM: Institut Franpis Rio Madeira, originating in the eastern Peruvian and de Recherche Scientifique pour le Développement en Bolivian mountain ranges. The regional sediment bud- Coopération; SENAMHI: Servicio Nacional de get of the Madeira river bisin shows that more than Meteorología e Hidrología de Bolivia; UMSA: 50% of the suspended yield exported by the Andes Universidad Mayor de San Andrés, La Paz, Bolivia will sediment in the Amazonian floodplain (Guyot et (Guyot, 1993), and during hydrobiological studies al. 19S8, 1989). (Wasson and Marin, 1992). This large and relatively pristine basin presents a wide range of climatic and geomorphological features. Altitude varies from 6500 to 120 m, and rainfall ranges 2. Study area from 200 to more than 6000 mm yr-’. In the Andes, individual watersheds are heavily contrasted; they The Bolivian part of the Rio Madeira drainage range from semi-arid, highly erodible basins incised in basin (Fig. 1) covers, 903,500 km2, extending over the the Altiplano Tertiary-Quaternary sedimentary series Andes (25%), the Brazilian shield (27%), and the (such as the Rio La Paz watershed), to densely vege- Llanos (48%). At the Brazilian frontier (Villabella), tated hyper-humid basins on Palaeozoic rocks (such as mean annual discharge of the Rio Madeira is the “Yungas” valleys), or Tertiary sedimentary series I2 401-410 J.L. Guyot et al. IJolirital of South Atnerican Earth Sciences (1999) 403

Fig. 2. Sediment sampling points localisation in the Andean Rio Alto-Beni drginage basin (see Tables 1 and 2 for station codes). in the Alto-Beni foothills. The Bolivian Llanos is a flat the Andean range, which is the main source of the plain of recent alluvial sediments, whose level is con- sediment yield. trolled by the Precambrian Brazilian Shield outcrops upstream of Villabella. About 150,000 km’ are flooded annually in this region (Roche and Fernandez, 19SS). 3. Methodology Sediments have been sampled in these three main valley types, and will be referred to in the following 3.1. Bed sediments text as (1) “semi-arid” for the Rio La Paz and tributaries, and (2) “Yungas” for the Rio Huarinilla- The granulometry of coarse bed sediment in the Coroico-Kaka stem; the Rio Alto-Beni drains both Andes was determined in situ by a “rope” method de- types and (3) “Llanos” for the Amazonian floodplain rived from Wolman (1954). A graduated rope is placed rivers (see Fig. 2). All the rivers sampled originate in randomly within (if possible) or nearby the stream bed 12 (1999) 401-410 404 J.L. Guyot et al./ Journal of South Americati Earth Sciences

Table 1 River station characteristics and river bed sediment median diameter (dso)

Code River station Altitude (m) Distance from Villabella (km) d50 ("1 c1 Rio Huarinilla near the Cumbre 4000 1115 193 c2 Rio Huarinilla at the Inca bridge 2900 1110 226 c3 Rio Huarinilla at'Choro 2000 1100 130 c4 Rio Huarinilla at Chairo 1300 1085 187 CS Rio Coroico at San Pedro 650 1050 144 CG Rio Coroico at IBTA Station 600 1035 84 c7 Rio Coroico at Santa Fe 500 1020 12 C8 Rio Coroico at Alcoche 450 1010 63 KK Rio Kaka at Puerto Pando 380 920 58 LI Rio Achumani at La Paz 3550 1200 28 L2 Rio La Paz at Puente Lipari 2950 1240 27 L3 Rio Palca at Tahuapalca 2400 1225 64 L4 Rio La Paz at La Plazuela 800 1135 25 BA Rio Alto-Beni at Chepite 300 850 32 AB Rio Beni at Angosto del Bala 280 810 35 B2 Rio Beni 260 805 57 B3 Rio Beni 240 796 26 B4 Rio Beni 220 785 0.13 B5 Rio Beni 200 710 0.10 BG Rio Beni I90 570 0.15 B7 Rio Beni 180 445 0.09 BS Rio Madidi 180 427 0.10 B9 Rio Beni I60 340 0.1 1 PC Rio Beni at Portachuelo 150 200 0.09 at low flow. 'Space between rope graduations is about through an ultrasound tank. Particle-size distribution twice the diameter of the largest elements.of the sedi- analyses were then performed on the suspension, using ment. Each element found under a graduation is a laser grain-size measuring device (3600E Malvern measured by passing it through a granulometer, which model) in the Bordeaux University Laboratory is analogous to a sieve series in geometric progression (France). according to the Phi scale (with half-Phi graduation). The suspended sediment samples of Beni and The grain size of the finest elements is referred to as Mamore rivers in the Llanos were provided by the fine gravel (2-8 mm), coarse sand (0.5-2 mm), fine PHICAB Network during the 1986-87 period. For the sand (0.5-0.062 mm), or silt (<0.062 mm) by a visual Andean rivers, suspended sediments were collected comparison with sieved sediment. 50 elements are during the March 1988 flood period. measured by sample (Kellerhals and Bray, 1971) and sampling is replicated 2-5 times according to the apparent heterogeneity of the substrate. In the larger 4. Results and discussion Llanos rivers with sandy substrate, the grain size was obtained by the classical method of sieving and weigh- 4.1. Bed sedinients ing of a river bed sediment sample, in the SENAMHI Laboratory (El Alto, Bolivia). A noticeable differkce appears between the bed In situ granulometric measures and river bed sedi- sediments of the two main valley types (Table 1). In ment samples were collected from the Rio Beni drai- the Yungas, along the Huarinilla-Coroica-Kaka river nage basin during the 1988 and 1989 low flow periods. transect (from 4000 to 380 m - C1 to C&, KK - Fig. 2), d50 values decrease normally fro& 200 to 3.2. Susyetided matter 60 mm (Fig, 3), indicating the progressive settling of largest particles. In the semi-arid valley, alopg the La At the PHICAB stations in the Llanos (Fig. l), sus- Paz-Palca-Alto Beni river stem (from 3550 to 300 m - pended sediment samples were collected near the sur- - L1 to L4, LU, AI - Fig. 2), no significant dS0 vari- face, in the middle of the river. Measurements made ation is observed downstream, suggesting a mass trans- with depth integrating samplers at gauging stations port of unsorted sediment. This is due to the exhibited good homogeneity of suspended sediments particular granulometric composition of the sediments over the whole cross-section (Guyot, 1993). The sedi- in these basins. Some samples (L3 and L4) showed ments collected on filters were extracted by passing two main modes, one of which corresponds to a stock Guyot et al. Joiirnal of Soiìtli Antericati Earth Sciemes 12 401-410 J.L. 1 (1999) 405

100 ......

-CI Rio Coroico - Kaka ---_ Andes c2 ...... c3

c4 % 50 c5

-D- C6 --A-- c7 ...... Ca .. - .-.- KK O

0.01 0.1 1 10 100 1000 mm

100 1- ...... i;*,.-? ...... Rio La Paz - Alto Beni Andes

% 50 -...... - .-. - L4 -.._BA

+--+i 7 OtO ---- 8

0.01 o. 1 1 10 I60 1O00

IO0 -AB ---o-- 82

...... 83 ---o---EM *..- % 50 85 e6 07 ...... I36 .. -. -. - 09

O 0.01 o. 1 1 10 IO0 1000 mm

Fig. 3. River bed sedimentary granulatory of the Rio Beni drainage basin (see Table 1 for station codes). i

406 J.L. Guyot et al. 1Journal of South American Earth Sciences 12 (1999) 401-410

5000 I ANDES 1 I 4Oo0 $ Rio Coroico i i \ I Kaka i i i

, .. _-- - .. lo00

~ , c O 1500 1250 loo0 750 500 250 O Distance from Villabella (km)

1000

s,o o ...... tl' ...... I...... U :A La Paz - Alto Beni -0 O y. O ...... IO % ...... Andes limit

A ...... A...... !._____a...... a

I :i , 0.01 1500 1250 1000 75d 500 250 O Distance from Villabella (km)

...... FI r1 n ...... E

.....~ ...... 0.1 o ...... Andeslimit o .I

0: ...... _____..______._.___...... >...... 5...... r-0.01 d. ., u) ua3

0.001 1500 1250 1 O00 75b 500 250 O Distance from Villabella (km)

Fig. 4. Longitudinal section, river bed and suspended sediment median diameter (d50) of the Rio Beni drainage basin. J.L. Guyot et al. I Journal of Soiith Aniericari Earth Scietices I2 (1999) 401-410 407

Table 2 River station characteristics and suspended sediment median diameter (d5")

Code' River station Altitude (m) Distance from Villabella (km) Number of samples dSo(pm) dgo (pm) dto (pm)

LI Rio Achumani at La Paz 3550 1200 1 26 L4 Rio La Paz at La Plazuela 800 1135 1 92 LU Rio Luribay at Luribay 2550 1210 1 95 CO Rio Consata at Consata 900 1085 1 81 AI Rio Alto-Beni at Angosto Inicua 390 950 1 17 AB Rio Beni at Rurrenabaque 280 810 4 11.0 3.4 39.8 PC Rio Beni at Portachuelo 130 200 4 12.0 3.4 41.2 CE Rio Beni at Cachuela Esperanza 120 30 4 9.4 3.1 37.0 AP Rio Grande at Abapo 450 1725 4 7.1 2.9 20.5 PV Rio Ichilo at Puerto Villarroel 170 1487 4 12.7 4.0 36.5 PG Rio Mamore at Puerto Ganadero 140 920 39 9.0 3.0 33.9 PS Rio Mamore at Puerto Siles 130 436 36 8.1 2.9 28.0 GM Rio Mamore at Cuayaramerin 120 55 3 9.4 3.1 32.0 ' L1, L4, LU, CO and AI data from Barragan, 1990. of fine sand (10.1 mm) and the other, to a coarse of downstream fining. The mean value of the median stock (> 10 nim). Such bed sediments are highly un- grain size of the Rio Beni bed sediments in the Llanos stable, and scoured very frequently due to the energy is 0.11 mm; this value is consistent with Taborga's of these high gradient streams (slope >3%), as evi- data (1964) for the Beni river. The samples of the Rio denced by the scarcity of the benthic fauna (Wasson Mamore and its tributaries, from the Andean pied- and Marin, 1992). This particularity is due to the fine mont to Guayaramerin, show a more regular decrease sediment load of the Andean rivers (rios La Paz, of particle sizes. The d50 of the Mamore sediments in Sapahaqui and Luribay) which drain the highland qua- the Llanos range from 0.02 to 0.08 mm, with an aver- ternary basin of the Altiplano. age of 0.04 mm (Taborga, 1963). The d5o of the Rio Other data obtained from bed load sampling in the Mamore bed sediments is three times smaller than that same region seems to corroborate these findings. In the of the Rio Beni. Such sediment characteristics are Yungas valley, the d50 of the material transported is explained by the difference in gradient between the two 26 nim for the Rio Unduavi at Sirupaya (alt. 1600 m streams, as well as the extent of their flood plains, - ENDE, 1980), lower than the bed sediment d50 which are seven times larger in the case of the Rio values for the same altitudinal range in our data Mamore basin (Roche and Fernandez, 1988). (Table 1). Conversely, bed load sampling on the The median ldiameter of bed sediment particles in Archumani and Huayllani rivers, two tributaries of the the Bolivian Llanos rivers flowing out from the Andes Rio La Paz, resulted in d50 values ranging from 3 to (around 0.1 mm) appears to be lower than in other riv- 80 mm during flood events, with an average of 25 mm ers in the Amazonian range: 0.25 mm for the Amazon, (Bourges et al., 1995), very close to the bed sediment 0.4 mm for the Orinoco, and 0.34 mm for the Rio d50. Guapore-Itenez (Taborga, 1967), a tributary of the The most abrupt discontinuity in the bed sediment Rio Mamore which drains the Brazilian shield. The composition occurs at the transition between the coarser sediments of the Rio Itenez may be explained Andes and the Llanos. Sites located before the outflow by ancient hydraulic conditions, since present day cur- of the Andes (BA and AB - Fig. 2) have a bed sedi- rent suspended matter concentrations are always very ment made of gravel and pebbles with d50 near 30 mm. low (an average 30 mg/l, which made grain-size analy- As the Rio Beni enters the Llanos, the same granulo- sis very difficult). metric composition of the bed sediment is observed on the first 20 km (B2 and B3), but then the median di- 4.2. Suspended niutter ameter decreases drastically over 10 km (Fig. 4), to remain remarkably stable thereafter along the next In the Andes, the grain size distribution of sus- 800 km with a djo ranging from 0.09 to 0.15 mm. pended sediment has been determined by means of The same stability over long distances has been samples taken from some tributaries of the Rio Beni observed in other large tropical rivers, such as the during the March 1988 flood period (Barragan, 1990; Amazon and the Orinoco (Nordin et al., 1980; Mertes Guyot et al., 1993). Suspended sediments seem to be and Meade, 1985). In fact, particle-size distribution of made up of fine sands and silts, although the clay frac- sediments varies from one site to another on a given tion always exceeds 10%. The median grain size in stream, but there does not seem to be an overall trend such suspensions varies between 0.02 and 0.10 mm J.L. Guyot et al. Jorlrnal of South Americi n Earth Sciences 12 (1999) 401-410

1 10 100 IOW 1 10 100 Sedimant (p) Suspendend Sediment Gain size (pm) Suspended Grain Size

.. 1 10 100 1OW 1 10 1M 1MM (pm) Suspended Sediment Grain Size (pm) suspended Sediment Gain size

......

-. 1 10 100 low 10 IW 1MM suspended Sediment Suspended Sediment Grain Size (pm) Grain Size (pm) .. .:I.:-

loo0 1 10 100 1 10 1w suspended (pm) Suspended Sediment Grain Slze (pm) iI sedinent Grain sire 2 Fig. 5. Suspended sediment granulometric curves of the PHICA gauging stations in the Llanos (see Table for station codes).

(Table 2), which is the samle order of magnitude of the particularity is due to the fine fraction of the Altiplano bed sediments in the Amazon plains. From upstream quaternary sediments. to downstream, suspended sediment d50, progressively In the Llanos, the results obtained during the 1986- decreases (Fig. 4), except for the Rio Achumani (L1 87 hydrological year indicate that, over the whole - Fig. 2), which has a low d50 value at 3550 m. This basin, suspended matter is essentially silt and the per- \

A J.L. Guyot et al. Journal South American Earth Sciences 12 (1999) 401-410 \ 1 of 409 75 - O 50 Y al d50 ._N v1 - &O E I- 0 dl0 E 25 - o

O O 2000 4000 6000 8000 Discharge (m3.s-1)

75 ,.."".."......

nE ìo 50 ...... Ya 18 ,. O d) ._N u) o o ," o O C 00 .- 0 d10 E 25 o O 7

O o -_ - O -I I O 1 O00 2000 3000 Suspended sediment (mg.1-1)

Fig. 6. Suspended sediment grain size vs discharge and suspended sediment load, Rio Mamore et Puerto Ganadero (PG).

centage of fine sands is always low. The suspended Congo, it varied from 9 to 14 pm (Jouanneau et al., sediment d50 value in the Amazonian plain presents no 1990). Like river bed sediments, suspended sediment significative variation from upstream to downstream. particle size does not vary much from upstream to The transition from the Andes to the Llanos is not as downstream. The suspended sediment's diameter in the marked as for the bed sediments (Fig. 4). two large rivers (Rio Beni at Cachuela Esperanza and Systematic grain-size analyses of suspended sediment Rio Mamore at Guayaramerin - CE and GM - Fig. for the complete 1986-87 hydrologic year have been 1) is similar (d50= 9 pm), equivalent to approximately carried out using samples taken at 10-day intervals at one-tenth of the bed sediments diameter. two stations on the Rio Mamore (PG and PS - Fig. 1). Results show little variation throughout the year (Fig. 5) and no relation between distribution of grain- 5. Conclusion size fractions and discharge or suspended sediment load (Fig. 6). This first insight into the granulometric composition The mean median grain size of suspended sediment of river bed and suspended sediments in the Bolivian was similar at all stations in the Llanos, and varied Rio Madeira drainage basin has shown a clear distinc- from 7 to 13 pm (fine silts). The median grain size of tion and a very sudden transition between the Andes suspended matter varied from 2 to 20 pm in the and the Llanos. Amazon (Meade, 1985) and from 6 to 16 pm in the Emphasis must be given to the transition zone at the Rio Paraná (Drago and Amsler, 1988), whereas, in the Andean piedmont; a strongly subsident area, which is ,

401410 , 410 J.L. Gtfyot et al. 1Journnl of South American Earth Sciences 12 (1999)

the preferential accumulation zone for the coarse ma- hidroeléctrico Sakhahuaya, Hdrologia y sedimentologia. ENDE, teriaí of Andean origin. Only the fine particles are Cochabamba, Bolivia, 121 pp. Guyot, J.L. 1993 Hydrogéochimie des fleuves de l’Amazonie bolivi- transported towards the Amazon, with the flood plains enne. Coll. Etudes et Thèses, ORSTOM, Paris, France, 262 pp. playing a regulating role in the transfer. This explains Guyot, J.L., Bourges, J., Hoorelbecke, R., Roche, M.A., Calle, H., the homogeneity of bed and suspended sediment grain Cortes, J., Barragan, M.C., 1988. Exportation de matières en sus- s size over several hundreds of kilometers, in both the pension des Andes vers l’Amazonie par le Rio Béni, Bolivie. In: Beni and the Mamore rivers, and the lack of relation- Bordas, P., Walling, D.E. (Eds.), Sediment budgets. IAHS, ship between river discharge and grain size distribution Wallingford, UK, pp. 443-451 174. Guyot, J.L., Bourges, J., Calle, H., Cortes, J., Hoorelbecke, R., in the lower part of these rivers. Roche, MA., 1989. Transport of suspended sediments to the Within the Andean range, the two main geomorpho- Amazon by an Andean river: the River Mamore, Bolivia. In: logical valley types referred to as “semi-arid” and River Sedimentation. IRTCES, Beijing, China, pp. 106-1 13. “Yungas” sampled in our study also exhibited distinct Guyot, J.L., Jouanneau, J.M., Quintanilla, J., Wasson, J.G., 1993. granulometric characteristics, corresponding to differ- Les flux de matières dissoutes et particulaires exportés des Andes par le Rio Béni (Amazonie Bolivienne), en période de crue. ent sediment structure and transport processes. Such . Geodinamica Acta 6 (4), 233-241. differences are reflectsed in substratum stability and Jouannesu, J.M., Lapaquellerie, Y., Latouche, C., Tastet, J.P., 1990. water quality, and have important biological impli- Résultats préliminaires de la campagne Oubangui-Congo de cations. Thus geomorphological valley type appears to Novembre 1988. Bull. des Sciences Géologiques 43 (l), 3-14. be a relevant descriptor of river functional types in Kellerhals, R., Bray, D.I., 1971. Sampling procedures for coarse fluvial sediments. American Society of Civil Engineers 97, 1165- aquatic ecology. 1179. Meade, R.H., 1985. Suspended Sediment in the Amazon River and its Tributaries in Brazil during 1982-1984, US Geological Survey Acknowledgements Open File Report 85-492, Denver, USA, 39 pp. Mertes, L.A.K., Meade, R.H., 1985. Particle sizes of sands collected We acknowledge Calle (SENAMHI, El Alto, from the bed of the Amazon River and its tributaries in Brazil H. during 1982-84, US Geological Survey Open File Report 85-333, Bolivia) for granulometric determinations on river bed Denver, USA, 16 pp. sediments, G. Hanaut (Univ. Bordeaux, France) for Molinier, M., Guyot, J.L., Calli.de, J., Guimarges, V., Oliveira E, granulometric determinations on suspended sediments, Filizola, N., 1997. Hydrologie du bassin amazonien. In: Théry, and J.F. Dumont (ORSTOM, La Paz, Bolivia) for H. (Ed.), Environnement et développement en Amazonie brésili- river bed sediments in situ measures. enne. Belin, Paris, pp. 24-41. Nordin, C.F., Meade, R.H., Curtis, W.F., Bósio, N.J., Landim, P.M.B., 1980. Size distribution of Amazon River bed sediment. Nature 286, 52-53. References Roche, M.A., Fernandez, C., 1988. Water resources, salinity and salt yields of the rivers of the Bolivian Amazon. 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Tomo III: Cuenca 1995 (l), 111-126. des Rio Itenez. Fuerza Naval Boliviana, La Paz, Bolivia, 77 pp. Drago, E.C., Amsler, M.L., 1988. Suspended sediment at a cross sec- Wasson, J.G., Marin, R., 1992. Tipología y potencialidades biológi- tion of the middle Paraná river: concentration, granulometry and cas de los rios de altura en la región de La Paz (Bolivia). influence of the main tributaries. In: Bordas, P., Walling, D.E. Memoria de la Sociedad de Ciencias Naturales La Salle 48, 97- (Eds.), Sediment budgets. IAHS, Wallingford, UK, pp. 38 1-396 122. 174. Wolman, G., 1954. A method of sampling coarse river bed material. ENDE, Empresa Nacional de Electricidad SA, 1980. Proyecto Trans. Amer. Geoph. Union 35 (6), 951-956.